This invention generally relates to a thermometer that measures a temperature of an object to be measured in a noncontact manner and more particularly relates to a clinical thermometer that measures a temperature of an eardrum by inserting an end of a probe into an ear.
For convenience of explanation, a typical conventional ear-type clinical thermometer will be described below by referring to FIGS. 8 and 9. FIG. 8 is a schematic block diagram of a conventional ear-type clinical temperature, illustrating a principle of operation. FIG. 9 is a longitudinal section view of an end portion of a probe in a typical conventional ear-type clinical thermometer. As shown in FIGS. 8 and 9, a probe 10 of a typical conventional ear-type clinical thermometer utilizes a thermopile 11. In general, a thermopile creates an electric potential difference (Seebeck effect) by a difference of temperature between a cold junction and a hot junction on the thermopile. In order to utilize the thermopile as a probe for measuring a temperature, it is necessary to effect a compensation of a room temperature (an environmental temperature), as is the case with a thermocouple. Thus, the conventional ear-type clinical thermometer has used a thermistor 12.
When a temperature in an object being measured is equal to a temperature in a cold junction on the thermopile 11, an output from the probe 10 is zero (zero point). On the other hand, when a temperature in an object being measured is higher than a temperature in a cold junction on the thermopile 11, an output from the probe 10 becomes great nonlinearly.
In the case where the probe 10 measures a body temperature, an output from the probe 10 is a very feeble level. Consequently, it is necessary for a signal amplifier 13 to amplify the output from the probe 10 to a level to which a signal processing can be applied. Further, it is necessary for a linearizer 14a to linearize the nonlinear output. On the other hand, since an output from the thermistor 12 is nonlinear, a linearizer 14b must linearize the output from the thermistor 12.
Under a stable condition of an environmental temperature, a temperature in the thermistor 12 is equal to a temperature in a cold junction on the thermopile 11. A signal linearized from the output of the probe 10 indicates a difference between the temperatures in the thermistor 12 and in the object being measured. Accordingly, it is possible to obtain the temperature of the object being measured by correcting the environmental temperature by a temperature conversion device 17 after correcting the signal linearized from the output of the probe 10 by an emittance correction device 15 and effecting a compensation of room temperature or a compensation of cold junction temperature of the corrected signal and the linearized signal from the thermistor 12 by an adding device 16. This will be displayed on a display 18.
Since the thermopile has an unstable sensitivity in individual differences, the output voltage is unstable, even if there is a certain difference of temperature. Thus, it is necessary to individually effect an adjustment of sensitivity (correcting operation) for a probe using a thermopile. Although an infrared absorption membrane for the thermopile (a portion 116 integrated with the infrared absorption membrane and hot junction in FIG. 9) increases a temperature by absorption of infrared rays, a package of the thermopile also radiates infrared rays onto the infrared absorption membrane. In a common using method, the package is deemed to be at the same as the temperature of a heat sink (heat absorption section) in the thermopile. However, when the package is subject to an abrupt change of temperature due to an external factor, a difference of temperature will be caused between a head portion of the package and the heat sink of the thermopile and the probe will output an unstable voltage transiently.
Consequently, in order to apply a uniform and moderate change of temperature to the probe 10, as shown in FIG. 9, a thermopile 110 is disposed in a holder 111 made of a metal having a good heat conduction (for example, aluminium) and the holder 111 is sheathed by a cover 114 so as to enclose the thermopile 110 by an air layer 112 and a resin 113 that serve as an heat insulation material. A metal tube 115 is provided on a front side of the thermopile 110 to reduce affection of heat radiation from the object being measured (human body). The metal tube 115 is plated with gold to reduce an emittance as low as possible and to serve as a wave-guide. Although a semiconductor, a thermistor, or the like is usually utilized as a sensor for compensating a temperature of the cold junction, the thermistor has been commonly used on account of a low cost in production and a high precision.
In the case where a heat coupling between the cold junction on the thermopile and the thermistor is poor, a difference of temperature is caused and it is impossible to effect a precise measurement. A thermistor (not shown) is mounted in a package together with the thermopile to enhance a heat coupling between a heat sink of the thermopile cold junction and the thermistor. Since a B constant (resistant temperature characteristics, that is, a constant for indicating a change of a resistant value obtained from temperatures at any two points) is unstable even if any thermistors have the same standard, it is difficult to maintain a precision within a wide range of environmental temperature. For example, in the case where a thermistor in an electronic clinical thermometer measures a body temperature within a range of 34 to 42° C., a precision of the thermistor may be maintained within a range of 8° C. However, in the case where a range of environmental temperature in the thermopile is set to be within a range of 5 to 40° C., a precision of the thermistor must be maintained within a range of 35° C. (40−5=35).
A structure of the probe 10 shown in FIG. 9 causes a difference of temperature between the thermopile 110 and a distal end of the probe 10 during increase of the environmental temperature. The probe 10 will generate a positive error, since a temperature at the distal end of the probe 10 is higher than that of the thermopile 110. The probe 10 causes a difference of temperature between the thermopile 110 and the distal end of the probe 10 during decrease of the environmental temperature. The probe 10 will generate a negative error, since a temperature at the distal end of the probe 10 is lower than that of the thermopile 110. In order to reduce such errors, the cover 114 encloses the thermopile 110 to lower affection of a temperature change. However, an oversize of the metal holder 111 is limited on account of the object being measured. A countermeasure against the errors due to the change of environmental temperature takes a correction of an output of the probe by calculating a rate of change per time concerning the thermistor in the thermopile package, thereby reducing the errors.
A first object of the present invention is to provide an ear-type clinical thermometer that can eliminate affection due to a change of environmental temperature during a short period of time and does not generate an error due to a change of environmental temperature.
A thermistor is used to compensate a temperature in a cold junction on a thermopile utilized in an infrared clinical thermometer. Although it is easy to adjust the characteristics of the thermistors in the limited range of temperatures, as is the case where the thermistor is used in an electro clinical thermometer, it will be difficult to adjust the characteristics in a wide range of temperatures in the case where the thermistor is used in a clinical thermometer. Accordingly, a second object of the present invention is to provide an ear-type clinical thermometer that can ensure a precision within a wide range of environmental temperature.
The thermopile requires a correcting operation to maintain a precision, since the thermopile has great individual differences. A correcting operation of the thermopile will invite a high cost in production. Accordingly, a third object of the present invention is to provide an ear-type clinical thermometer that can require no correcting operation or achieve a greatly simplified correction in comparison with a thermopile system.
When a conventional ear-type clinical thermometer measures a body temperature under a lower temperature environment, a probe of the thermometer will cool an external acoustic meatus. Although a precision of measurement at the first time will be considerably good, indications of measurement after a second time or later without taking much time are likely to be lower. Consequently, measured values in the conventional ear-type clinical thermometer will be unstable on account of affection of environmental temperatures. Accordingly, a fourth object of the present invention is to provide an ear-type clinical thermometer that can eliminate unstable indications due to affection of environmental temperature.